Method op making hot tops for ingot molds



Nov. 16, 1965 P. DAVIDSON METHOD OF MAKING HOT TOPS FOR INGOT MOLDSOriginal Filed March 3. 1961 Reissued Nov. 16, 1965 25.905 METHOD OFDIAKING HOT TOPS FOR INGOT MOLDS Per Davidson, Sandviken, Sweden,assignor to Sandvikens Jernwerks, Aktiebolag, Sandviken, Sweden, aSwedish corporation Original No. 3,123,878, dated Mar. 10, 1964, Ser.No. 93,133, Mar. 3, 1961. Application for reissue Jan. 5, 1965, Ser. N0.438,447

Claims priority, application Sweden, Oct. 4, 1960, 9,444; Get. 26, 1960,10,263 4 Claims. (Cl. 22193) Matter enclosed in heavy brackets appearsin the original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This application is a continuation-in-part of my application Serial No.861,098, now U.S. Patent No. 3,072,981, filed Dec. 21, 1959.

The present invention relates to hot tops for ingot molds for castingsteel and other metals.

The invention resides in a thin inner disposable sleeve of a particularcompostion to be described more fully hereinafter and an outer sleevewhich serves to position and support said inner sleeve.

For a long time there has been a need for a hot top for ingot moldswhich is inexpensive both as to the cost of its ingredients orcomposition and as to the cost of its production, which will providegood heat insulation for the cast metal and give a smooth surface on thecast metal, free of insertions, fins, blisters and the like and whichhas good shape permanence and storing properties. Hot tops heretoforeavailable generally have lacked one or more of these desirablequalities.

The present invention provides a hot top having the desirable qualitiesenumerated above and other advantages which will be referred to in thefollowing description.

In accordance with the present invention the inner sleeve of the hot topis formed by depositing a layer of the desired thickness of the solidcomponents of a composition consisting essentially of 82 to 94% byweight of a finely divided refractory or fire-proof material such asquartz or silicon compounds such as silicates, olivine or magnesite, 3to 9% by weight of an organic fibrous material such as cellulose, paperpulp, waste paper pulp or the like, 1 to 8% by weight of a binder suchas an organic glue, up to 2.5% by weight of a mineral fiber materialsuch as absestos, glass wool or the like and water or other suitableliquid in quantity sufficient to give a suspension or slurry, upon aporous mold. The soformed layer, after being sucked sufficiently free ofliquid to be self supporting is stripped from the mold and dried andbaked at a temperature of from 120 to 200 C., preferably l40-l60 C.

The inner sleeve, made as described above, generally is frusto-conicalin shape and is in a single piece but the invention embraces sleeves ofother shapes, e.g., cylindrical as Well as sleeves of all shapes formedin two or more pieces adapted to be fitted together to provide thedesired shape.

The inner sleeve described above, when molded as described, has a porousinternal structure which is held together by the fibrous ingredients ofthe composition, and a relatively smooth hard surface or surface layer.This is important as will appear hereinafter principally because itpermits the production of castings having a smooth surface in thatportion thereof within the hot top.

The hot top inner sleeve made as described above is placed on the ingotmold so that its lower edge bears tightly against the inner surface ofthe mold adjacent the upper end thereof. In order to attain a tight fitbetween the inner sleeve and the ingot mold the lower edge of the sleevepreferably is beveled or chamfered so that the beveled surface bearsagainst the surface of the mold. Generally the walls of the mold divergeupwardly at least adjacent the top of the mold and the beveled surfaceof the sleeve will rest upon this outwardly divergent surface of themold. Preferably the surface of the mold at least adjacent the upper endis at an angle to the axis of the mold of at least 2 and the angle maybe as great as 10 or more but preferably within the range from 4 to 8".With such an outwardly inclined mold surface and the lower edge of thesleeve beveled at a corresponding angle a tight joint between the moldand the sleeve is provided and the formation of fins which is quitecommon with hot tops heretofore available is avoided.

After the inner sleeve has been placed upon the mold as described abovean outer sleeve of about the same height as the protruding portion ofthe inner sleeve and of the same size and shape is placed on top of themold over the inner sleeve. This outer sleeve which is made of metal orother durable material and has considerable thickness and weight servesto hold the inner sleeve in place during a casting operation andparticularly to prevent the inner sleeve from being displaced upwardlyby the pressure of the liquid metal being cast. After a castingoperation has been completed the inexpensive inner sleeve is discardedwhile the outer supporting sleeve is saved for repeated use.

The invention will now be described in greater detail in connection withthe accompanying drawings which illustrate an embodiment of theinvention.

Referring to the drawings:

FIG. 1 is a vertical sectional view of the upper end of an ingot moldand the associated hot top,

FIG. 2 is a similar sectional view of only the upper left hand side ofan ingot mold and the associated hot top showing a modificationincluding a suitably positioned mass of exothermic material, and

FIG. 3 is a view similar to FIG. 2 showing another modificationincluding an annular supporting liner positioned around the lower end ofthe hot top.

In the drawings 12 is the ingot mold having upwardly divergent surfaces14 adjacent the upper end thereof. 10 is the hot top inner sleevedescribed above which, as stated, may be in one piece or formed of twoor more pieces fitted together. 11 is the supporting outer sleeve. Thecomposition of the inner sleeve has been partially described above butit may be said here that the quartz ingredient of the composition neednot be pure quartz but may contain a minor proportion of the rockmaterial other than quartz normally associated with natural quartzdeposits. A variety of refractory materials may be substituted for thequartz such as olivine, magnesitc, dolomite, blast furnace and otherslags, sand and the like. The average grain size of the refractoryingredient of the composition i.e. the quartz or its equivalent is lessthan 1 mm., and preferably less than 0.3 mm. or even less than 0.2 mm.As a rule the refractory material is chosen with an average grain sizewithin the range from 0.6 to 0.05 mm. determined by the standardscreening method. The grain size of the refractory material may also bedescribed as being mainly less than mesh.

The organic fibrous ingredient of the composition, as stated above,preferably is cellulosic such as ground wood pulp, or so-calledmechanical pulp or pulp made from waste paper formed of such mechanicalpulp and may contain chemical pulp e.g. sulfate or sulfite pulp. Othersimilar organic fibrous materials may be used either alone or inadmixture with the wood pulp or paper pulp.

The organic glue ingredient of the composition may be a synthetic resinglue such as a urea or carbamide resin or silicone resin glue or a wellknown animal or vegetable glue or a cellulose derivative glue. It iseven possible to substitute the organic glue or binder, wholly or inpart by an inorganic binder such as water glass. The glue or bindergenerally is added to and mixed with the other ingredients in liquidform but it is also possible to mix the binder in finely divided solidform. Binder in liquid form generally is used in quantity within therange from 3% to 8% by weight while solid binder generally is used inquantity within the range from 1% to 4%.

The mineral fiber ingredient of the composition, e.g.

if used, is asbestos, rock wool or the like and generally is used inquantity within the range from 0.5% by weight to 2.5% by weight. Themineral fiber serves mainly merely to supplement the organic fibrousingredient and to increase the strength and durability of the hot topand may if desired be omitted entirely. As stated above the compositionfrom which the inner sleeve is formed, in the form af suspension orslurry, is deposited on a mold. For example a porous mold may bepositioned with one side immersed in the suspension and pressure appliedto the suspension and/or suction applied to the other side of the moldwhereby the liquid part of the suspension is forced through the mold andthe solids are deposited as a filter cake on the mold. The operation iscontinued until the desired thickness is obtained. Then, as stated, thefilter cake is removed from the mold and dried for from 1 to 5 hours,preferably 2 to 3 hours at a temperature of 120 to 200 0, preferably 140to 160 C. The molding and drying operations give the molded sleeve asmooth hard surface which may be attributed to the molding compositionused and/or to the drying operation but the drying temperature appearsto be an essential condition.

In a preferred embodiment of the invention the molding compositionconsists of from 85 to 91% of the finely divided refractory materialconsisting mainly of quartz, 3 to 9% and preferably 48% of organicfibrous material such as disintegrated waste paper, 1-7% and preferablyfrom 3 to 6% of synthetic resin glue such as a urea or carbamide resinand up to 2% and preferably from 0.4 to 1.5% of asbestos or itsequivalent.

In a specific embodiment the wall thickness of the sleeve 10 may bewithin the range from 5 to 15 mm. The lower edge 13 of the sleeve 10rests on the surface 14 of the ingot mold 12 and is supported externallyby the sleeve 11. The lower edge of the sleeve preferably is beveled orchamfered so as to provide an edge surface at the same angle as thesurface 14 of the ingot mold and thus to provide a better contactbetween the sleeve and the mold. The inclination of the chamferedsurface of the lower edge 13 and of the surface 14 is within the rangefrom 2 to 10, preferably 4 to 8, to the axis of the mold. It is withinthe scope of my invention to provide the ingot mold with an internalgroove or shoulder into or on which the lower edge of the sleeve restsin order to provide a tight joint between the hot top and the mold.

The sleeve 11, as shown in the drawings, is provided with a step orshoulder 15 which rests upon the upper surface 16 of the ingot mold andlimits its downward movement with respect to the mold and to the sleeve10. Thus the relatively fragile sleeve 10 will not be forced to supportthe whole weight of the sleeve 11 although these parts are designed sothat the sleeve 11, which is put in place after the sleeve 10, will holdthe latter down in firm contact with the mold. The sleeve 11 preferablyis formed of cast iron, concrete, cement, brick or the like, and may beunitary or made up of two or more pieces which fit together. It may beprovided with recesses or channels containing only air or a heatinsulating material such as asbestos. For instance the sleeve 11 mayconsist merely of an outer shell spaced apart from the sleeve 10 withthe space between said outer shell and the sleeve 10 filled with aninsulating and refractory material such as sand, brick or the like.

The sleeve 11 is provided with handles 17 to facilitate handling.

In practice is its advisable in some instances to use a packing materialsuch as sand, glass wool, rock wool, steel wool, asbestos, putty,cement, straw or the like in the joint between the sleeve 11 and themold 12 as shown at 18 in order to improve the tightness of the jointbetween the hot top and the mold.

The structures illustrated in FIGS. 2 and 3 are similar to that shown inFIG. 1 described above excepting that in the modification shown in FIG.2, the sleeve 10 is provided with an annular recess containing a layer19 of exothermic material. This exothermic material is ignited by theheat of the metal in the mold and serves to heat and thus to delay thesolidification of the molten metal adjacent the edge of the upper endthereof and thus to prevent or reduce the formation of a sink in the topof the ingot. A variety of exothermic materials or compositions areavailable such as a mixture of aluminum powder and iron oxide. Otherarrangements of the exothermic material are possible e.g. the exothermicmaterial may be merely applied to the surface of the sleeve Withoutproviding a recess therein or the whole upper end of the sleeve may be asection formed of exothermic composition.

In the embodiment shown in FIG. 3 a replaceable liner 20 of suitablematerial such as sheet iron, fitted into a recess in the wall of thesleeve 11 may be provided in order to improve the tightness of the jointbetween the mold and the hot top and to prolong the useful life of thesleeve 11.

Another modification which is illustrated in FIG. 3 is the omission ofthe thin, sharp edge formed between the chamfered surface 13 and theinner surface 21 so as to provide a rounded edge 22. This greatlyreduces breakage of the lower edge of the sleeve as it is handled instorage and use.

As has been indicated the sleeve 10 is first set on the ingot mold, andthe sleeve 11 is then lowered over it. The packing material 18 may beapplied either before or after or both before and after the sleeve 11 isapplied.

Specific examples of suitable inner sleeve compositions are as follows,the parts being in percent by weight.

l a i l) l c l d l e l i Paper pulp 5.3 6.2 6.0 l 7.5 9 O Binder(liquid) (3.4 4.2 5.2 6.5 7.0 Asbestos e- 1.5 0.5 0.8 1.0 1.5 Refractorymaterial 86.8 80.1 88.0 85.0 82.5 g l l Composition 0 is at presentpreferred.

Hot tops in accordance with the invention as described above giveexcellent results. The expandable inner sleeves thereof are inexpensiveboth as to the materials employed and the cost of manufacture. They havegood storing properties, i.e. they are sufficiently strong that ther isvery little breakage due to handling and they do not change shape orotherwise deteriorate in storage. They provide good heat insulation andgive castings with smooth surfaces and ingot tops which are free ofporosity. The outer sleeve 11 has a long life so that only inexpensiveparts are consumed i.e. the sleeve 10, the exothermic material 20, if itis used, and the packing 18. Pipes and segregations in the castings areminimized. This is of great economical importance because only a verysmall amount of the ingot head has to be returned to scrap metal. Forexample the yield of ingots made with the hot tops of the presentinvention is about 94% which is substantially greater than with otherhot tops heretofore commonly used.

It may be observed that the organic fibrous material facilitates thebinding together of the finely divided refractory material and at thesame time contributes a certain degree of porosity to the hot topstructure which enhances its insulating properties. At the same timeeither due to the limited quantity of organic material including binderuscd or to the porosity or both no 0bjectionable or harmful formationand liberation of gas occurs.

Regarding the thickness of the sleeve 10, which as stated may be withinthe range from 6 to mm., depending upon the size thereof, it may be saidthat a suitable thickness for a sleeve adapted to be used in casting a1.7 ton ingot is about 12 mm. The sleeve 10 generally is of uniformthickness but it is within the scope of my invention to vary thethickness, e.g. to make the sleeve thicker at the end adjacent to themold and thinner adjacent to the other end.

I claim:

1. Method of making a hot top disposable sleeve which comprises formingsaid sleeve out of a composition consisting essentially of from 82% to94% by weight of a finely divided refractory material having an averagegrain size within the range from 0.6 to 0.05 mm., from 3% to 9% byweight of an organic fibrous material and from 1% to 4% by weight of asolid organic binder material with sufiicient water to give a moldablemixture, and drying and baking the molded sleeve at a temperature withinthe range from about 120 C. to 200 C., said sleeve being formed byfiltering an aqueous slurry of the solid components of said compositionunder pressure through a porous mold.

2. Method as defined in claim 1 tion comprises from 0.5% to 2.5%inorganic material.

3. Method of making a hot top disposable sleeve which comprising formingsaid sleeve out of a composition consisting essentially of from 82% to94% by weight of a finely divided refractory material having an averagegrain size of less than about one mm., from 3% to 9% by weight of anorganic fibrous material and from 1% to 4% by weight of a solid organicbinder material with sufficient in which the composiby weight of afibrous water to give a moldable mixture, and drying and baking themolded sleeve at a temperature within the range from about C. to 200 C.,said sleeve being formed by filtering an aqueous slurry of the solidcomponents of said composition under pressure through a porous mold.

4. Method of making a hot top disposable sleeve which comprises formingsaid sleeve out of a composition consisting essentially of from 82% to94 by weight of a finely divided refractory material, from 3% to 9% byweight of an organic fibrous material and from 1% to 4% by weight of asolid organic binder material with sufficient water to give a nzoldablemixture, and drying and baking the molded sleeve at a temperature withinthe range from about 120 C. to 200 C., said sleeve being formed byfiltering an aqueous slurry of the solid components of said compositionunder pressure through a porous mold.

References Cited by the Examiner The following references. cited by theExaminer, are of record in the patented file of this patent or theoriginal patent.

UNITED STATES PATENTS MARCUS U. LYONS, Primary Examiner.

Disclaimer Reissue N0. 25,905.Per Davidson. Sandviken, Sweden. METHOD OFM\I\' ING HOT TOPS FOR IXGOT MOLDS. Reissue patent (lufed Xuv. 16, 1965.Disclaimer filed Apr. 13, 1970, by the asslgnee, iS'a'ndL'i/mms'Jeimrerlcs AB.

Hereby disclaims the terminal portion of the term of the patentsubsequent to Jan. 15, 1980.

[Ojficidl Gazette August 18, 1.970.]

